Vehicles have recently had doors locked, unlocked, opened, and closed via remote control with transmitters held by users from locations away for the vehicles, while also having the doors directly manipulated with mechanical keys. Receivers for receiving radio signals from the transmitters for such remote control are demanded to be inexpensive and to be manipulated reliably.
FIG. 5 is a block diagram of a conventional radio frequency (RF) receiver 20 disclosed in JP2002-218573A. RF receiver 20 includes antenna 1, band-pass filters 2 and 6, amplifiers 3 and 7, mixer 4, detector 8, and local oscillator 9. Antenna 1 is connected with band-pass filer 2. Band-pass filter 2 is connected with amplifier 3. Amplifier 3 is connected with mixer 4. Mixer 4 is connected with band-pass filter 6. Band-pass filter 6 is connected with amplifier 7. Amplifier 7 is connected with detector 8. Local oscillator 9 is connected with frequency multiplier 5. Multiplier 5 is connected with mixer 4.
Antenna 1, band-pass filers 2 and 6, amplifiers 3 and 7, mixer 4, detector 8, frequency multiplier 5, and local oscillator 9 constitute receiving section 15.
Controller 11 is connected with detector 8 and is implemented by a semiconductor device, such as a microcomputer. Oscillator 12 is connected with controller 11 and includes an oscillating element, such as a crystal oscillator. Controller 11 and oscillator 12 constitute control section 16.
RF receiver 20 includes receiving section 15 and control section 16.
RF receiver 20 is installed in a vehicle and connected with an electronic circuit and a battery mounted to the vehicle with connectors and lead wires. Controller 11 is connected with actuator 13 including actuating components, such as motor or solenoid, that actually perform a predetermined operation.
When a user manipulates a transmitter carried by the user who carries a mechanical key and is distanced away from the vehicle, the transmitter transmits a predetermined radio signal containing an identification code and an actuating code.
The radio signal transmitted from the transmitter is received by antenna 1 and supplied to band-pass filter 2. Band-pass filter 2 removes a noise other than a predetermined signal out of the received radio signal and outputs the predetermined signal. The output signal is amplified by amplifier 3 and is supplied to mixer 4.
Local oscillator 9 supplies an oscillation signal to frequency multiplier 5. Frequency multiplier 5 outputs, to mixer 4, a local oscillation signal having a frequency equal to integer multiple of the frequency of the oscillation signal output from local oscillator 9.
Mixer 4 mixes the predetermined signal with the local oscillation signal so as to produce a signal having a frequency equal to the sum of respective frequencies of the predetermined signal and the local oscillation and to produce a signal having a frequency equal to the difference between the frequencies of the predetermined signal and the local oscillation signal. Band-pass filter 6 outputs, as an intermediate frequency (IF) signal. The IF signal is amplified by amplifier 7, and detected by detector 8, thus being output as a detected signal.
The detected signal is supplied to controller 11 that operates based on a clock signal which is an oscillation signal supplied by oscillator 12. Controller 11 determines whether the detected signal is a locking signal or an unlocking signal. When the detected signal is the locking signal or the unlocking signal, controller 11 sends a control signal to actuator 13 so as to control actuator 13 to lock or unlock doors of the vehicle.
That is, the user can directly lock, unlock, open, and close the doors with the mechanical key while approaching the vehicle, and further, can lock, unlock, open, and close the doors remotely with the transmitter carried by the user from location distanced from the vehicle.
Receiving section 15 includes local oscillator 9 and oscillator 12 separate from each other. For example, if oscillator 12 is connected to frequency multiplier 5 and controller 11 simply with wiring, the signals supplied to frequency multiplier 5 and controller 11 can have too small amplitudes to allow controller 11 to operate, hence preventing the doors of the vehicle from being locked and unlocked.
In order to avoid such situation, amplifiers for amplifying the oscillation signal from oscillator 12 may be provided between controller 11 and oscillator 12 and between frequency multiplier 5 and oscillator 12. In this case, these amplifiers connected with oscillator 12 affects oscillator 12, and may stop oscillation of oscillator 12 including a crystal oscillator.
The oscillation frequencies of oscillators 9 and 12 are generally different from each other, thus preventing the oscillators from replaced as a single common oscillator and increasing cost.